Wearable health technology, particularly smartwatches, has revolutionized personal health monitoring by enabling continuous, non-invasive tracking of various physiological parameters. The potential applications of these devices in cardiology are extensive, but it is crucial to validate their accuracy against established medical-grade devices. The Apple Watch Series 9 (Apple, USA) exemplifies the capabilities of modern smartwatches, offering a wide range of health tracking features. These include heart rate monitoring, detection of irregular heart rhythms suggestive of atrial fibrillation, electrocardiogram recording, blood oxygen level measurement, and comprehensive mobility metrics (including VO2 max, six-minute walk distance, walking speed, step length, double support time, and walking asymmetry). Many of these parameters are highly relevant for cardiovascular patients, potentially aiding in disease progression monitoring and adverse event prediction. However, there is a lack of comprehensive validation studies for these devices in specific cardiovascular disease populations. This investigator-initiated prospective observational study involving 50-100 participants that aims to validate smartwatchbased assessments using medical-grade devices and techniques. The study will focus on adult patients with congenital heart disease, pulmonary hypertension, heart failure, and coronary artery disease, as well as athletes undergoing cardiovascular assessment. By comparing smartwatch data with established clinical measurements, the investigators seek to determine the reliability and potential clinical utility of these wearable devices in diverse cardiovascular contexts. This research will help bridge the gap between consumer-grade wearable technology and clinical practice in cardiology.